Issue 17: Convert ds key to core key

[AndrewSisley]

A fairly aggressive conversion of as many ds.Key references as I could to core.Key - including in files operating on the underlying datastores. This is partly because I'm assuming that the cost of core.Key{Key: foo} and core.Key.ToDS() is pretty minimal, and partly because I'm hoping to change core.Key into a more descriptive/safe set of types.

Feel very free to wait on the completion of the core.Key type change before reviewing if you think that this might have a notable negative effect on performance (or if you prefer a few more ds.Key refs for whatever reason).

[todo]

Config logger param package wide

defradb/merkle/clock/clock.go

Lines 42 to 45 in 0228369

	headset: newHeadset(headstore, core.NewKey(id)), //TODO: Config logger param package wide
	crdt: crdt,
	}
	}

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This comment was generated by todo based on a TODO comment in 0228369 in #18. cc @sourcenetwork.

[AndrewSisley]

Might be wasted effort reviewing this seperately now, will hopefully be putting up the key restructure PR soon (working, some cleanup left to do) which changes the same lines (plus some): https://github.com/sourcenetwork/defradb/tree/merkle-crdt-factory-key-fix-without-store-comp

[AndrewSisley]

Replaced by #19 (based off this branch)